Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751135AbdGIHXn (ORCPT ); Sun, 9 Jul 2017 03:23:43 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:59472 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750765AbdGIHXl (ORCPT ); Sun, 9 Jul 2017 03:23:41 -0400 Subject: Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing mirroring functionality To: Mike Kravetz , Anshuman Khandual , linux-mm@kvack.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org References: <1499357846-7481-1-git-send-email-mike.kravetz@oracle.com> <1499357846-7481-2-git-send-email-mike.kravetz@oracle.com> <3a43d5fa-223d-1315-513b-85d3a09a07b6@oracle.com> Cc: Andrew Morton , Andrea Arcangeli , Michal Hocko , Aaron Lu , "Kirill A . Shutemov" From: Anshuman Khandual Date: Sun, 9 Jul 2017 12:53:30 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <3a43d5fa-223d-1315-513b-85d3a09a07b6@oracle.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable x-cbid: 17070907-0048-0000-0000-00000252826D X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17070907-0049-0000-0000-00004803C29B Message-Id: <37f275bb-57c2-1485-02f2-dc71021f612a@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-07-09_04:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1703280000 definitions=main-1707090130 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1325 Lines: 26 On 07/07/2017 10:44 PM, Mike Kravetz wrote: > On 07/07/2017 01:45 AM, Anshuman Khandual wrote: >> On 07/06/2017 09:47 PM, Mike Kravetz wrote: >>> The mremap system call has the ability to 'mirror' parts of an existing >>> mapping. To do so, it creates a new mapping that maps the same pages as >>> the original mapping, just at a different virtual address. This >>> functionality has existed since at least the 2.6 kernel. >>> >>> This patch simply adds a new flag to mremap which will make this >>> functionality part of the API. It maintains backward compatibility with >>> the existing way of requesting mirroring (old_size == 0). >>> >>> If this new MREMAP_MIRROR flag is specified, then new_size must equal >>> old_size. In addition, the MREMAP_MAYMOVE flag must be specified. >> >> Yeah it all looks good. But why is this requirement that if >> MREMAP_MAYMOVE is specified then old_size and new_size must >> be equal. > > No real reason. I just wanted to clearly separate the new interface from > the old. On second thought, it would be better to require old_size == 0 > as in the legacy interface. That would be redundant. Mirroring will just happen because old_size is 0 whether we mention the MREMAP_MIRROR flag or not. IMHO it should just mirror if the flag is specified irrespective of the old_size value.